Browsing by Subject "Acoustic dispersion"

Now showing 1 - 3 of 3

Open Access
Collective modes in a quasi-one-dimensional, two-component electron liquid
(Pergamon Press, 1994) Tanatar, Bilal
Under favorable conditions, a new collective mode besides the usual plasmons may exist in degenerate electron-hole liquids. We calculate the dispersion and damping of this new mode (called the acoustic plasmon mode) in a quasi-one-dimensional, two-component electron liquid. We carry out our calculations first within the random-phase approximation, then include the effects of local-field corrections using a Hubbard-like approximation. The latter decreases the acoustic plasmon dispersion. © 1994.
Open Access
Lattice dynamics and elastic properties of lanthanum monopnictides
(2008) Gökoǧlu G.; Erkişi, A.
In this study, first principles calculation results of the second order elastic constants and lattice dynamics of two lanthanum monopnictides, LaN and LaBi, which crystallize in rock-salt structure (B1 phase), are presented. Calculations were based on plane wave basis sets and pseudopotential methods in the framework of Density Functional Theory (DFT) with generalized gradient approximation. Elastic constants are calculated by tetragonal and orthorhombic distortions on cubic structure. Phonon dispersion spectra was constructed in the linear response approach of the Density Functional Perturbation Theory (DFPT). The complete phonon softening with negative frequencies and large elastic anisotropy were observed for LaN single crystal as a sign of the structural instability. The phonon dispersion curve for LaBi is typical for lanthanum monopnictides and does not show any anomalous physical property. The calculated structural quantities for both LaN and LaBi systems agree well with the available experimental and theoretical data. © 2008 Elsevier Ltd. All rights reserved.
Open Access
Vibrational and thermodynamic properties of α-, β-, γ-, and 6, 6, 12-graphyne structures
(Institute of Physics Publishing, 2014) Perkgöz, N. K.; Sevik, C.
Electronic, vibrational, and thermodynamic properties of different graphyne structures, namely α-, β-, γ-, and -graphyne, are investigated through first principles-based quasi-harmonic approximation by using phonon dispersions predicted from density-functional perturbation theory. Similar to graphene, graphyne was shown to exhibit a structure with extraordinary electronic features, mechanical hardness, thermal resistance, and very high conductivity from different calculation methods. Hence, characterizing its phonon dispersions and vibrational and thermodynamic properties in a systematic way is of great importance for both understanding its fundamental molecular properties and also figuring out its phase stability issues at different temperatures. Thus, in this research work, thermodynamic stability of different graphyne allotropes is assessed by investigating vibrational properties, lattice thermal expansion coefficients, and Gibbs free energy. According to our results, although the imaginary vibrational frequencies exist for β-graphyne, there is no such a negative behavior for α-, γ-, and -graphyne structures. In general, the Grüneisen parameters and linear thermal expansion coefficients of these structures are calculated to be rather more negative when compared to those of the graphene structure. In addition, the predicted difference between the binding energies per atom for the structures of graphene and graphyne points out that graphyne networks have relatively lower phase stability in comparison with the graphene structures. © 2014 IOP Publishing Ltd.